Penkovsky joined the Soviet Red Army in 1937 and served as an artillery officer in World War II, being severely wounded in 1944. He attended the prestigious Frunze Military Academy in 1945–48. In 1949 Penkovsky transferred from the regular army to the Soviet army intelligence directorate (GRU). After attending the Military Diplomatic Academy (1949–53), he became an intelligence officer, serving primarily in Moscow. By 1960 he had become a colonel in the GRU and deputy chief of the foreign section of the State Committee for the Coordination of Scientific Research (1960–62), in which post his task was to collect scientific and technical intelligence on the United States, Britain, and other Western countries.

Penkovsky had in the meantime become increasingly disillusioned with the Soviet system, particularly with the leadership of Nikita Khrushchev. In April 1961, through Greville M. Wynne, a British businessman, he offered his services to British intelligence. Between April 1961 and August 1962 Penkovsky passed more than 5,000 photographs of classified military, political, and economic documents to British and U.S. intelligence forces. The information he provided on the Soviets’ relatively weak capability in long-range missiles proved invaluable to the United States before and during the Cuban missile crisis of October 1962. Penkovsky was in fact arrested by the Soviets on Oct. 22, 1962, at the height of that crisis, after they realized that highly classified information was leaking to the West.

Penkovsky was put on trial for treason in May 1963 and was found guilty and sentenced to death. According to an official Soviet announcement, he was executed on May 16, 1963, though other reports have him committing suicide while in a Soviet camp. In 1965 his journal, The Penkovskiy Papers, was published in the United States, though the book’s authenticity has been questioned by some.